A choir (/ˈkwaɪ.ər/) (also known as a chorale or chorus) is a musical ensemble of singers. Choral music, in turn, is the music written specifically for such an ensemble to perform.

A body of singers who perform together as a group is called a choir or chorus. The former term is very often applied to groups affiliated with a church (whether or not they actually occupy the choir) and the second to groups that perform in theatres or concert halls, but this distinction is far from rigid.

The term "Choir" has the secondary definition of a subset of an ensemble; thus one speaks of the "woodwind choir" of an orchestra, or different "choirs" of voices and/or instruments in a polychoral composition. In typical 18th- to 21st-century oratorios and masses, chorus or choir is usually understood to imply more than one singer per part, in contrast to the quartet of soloists also featured in these works.

Choirs are often led by a conductor or choirmaster. Most often choirs consist of four sections intended to sing in four part harmony, but there is no limit to the number of possible parts as long as there is a singer available to sing the part: Thomas Tallis wrote a 40-part motet entitled Spem in alium, for eight choirs of five parts each; Krzysztof Penderecki's Stabat Mater is for three choirs of 16 voices each, a total of 48 parts. Other than four, the most common number of parts are three, five, six, and eight.

Choirs can sing with or without instrumental accompaniment. Singing without accompaniment is called a cappella singing (although the American Choral Directors Association[1] discourages this usage in favor of "unaccompanied," since a cappella denotes singing "as in the chapel" and much unaccompanied music today is secular). Accompanying instruments vary widely, from only one to a full orchestra; for rehearsals a piano or organ accompaniment is often used, even if a different instrumentation is planned for performance, or if the choir is rehearsing unaccompanied music.

Many choirs perform in one or many locations such as a church, opera house, or school hall. In some cases choirs join up to become one "mass" choir that performs for a special reason. In this case they provide a series of songs or musical works to celebrate and provide entertainment to others.

Eastern Orthodox churches, some American Protestant groups, and some synagogues do not use instruments. In churches of the Western Rite the accompanying instrument is usually the organ, although in colonial America, the Moravian Church used groups of strings and winds. Many churches which use a contemporary worship format use a small amplified band to accompany the singing, and Roman Catholic Churches may use, at their discretion, additional orchestral accompaniment.

In addition to leading of singing in which the congregation participates, such as hymns and service music, some church choirs still sing full liturgies, including propers (introit, gradual, communion antiphons appropriate for the different times of the liturgical year). Chief among these are the Anglican and Roman Catholic churches; far more common however is the performance of anthems or motets at designated times in the service.

Mixed choirs (with male and female voices). This is perhaps the most common type, usually consisting of soprano, alto, tenor, and bass voices, often abbreviated as SATB. Often one or more voices is divided into two, e.g., SSAATTBB, where each voice is divided into two parts, and SATBSATB, where the choir is divided into two semi-independent four-part choirs. Occasionally baritone voice is also used (e.g., SATBarB), often sung by the higher basses. In smaller choirs with fewer men, SAB, or Soprano, Alto, and Baritone arrangements allow the few men to share the role of both the tenor and bass in a single part.

Male choirs, with the same SATB voicing as mixed choirs, but with boys singing the upper part (often called trebles or boy sopranos) and men singing alto (in falsetto), also known as countertenors. This format is typical of the British cathedral choir.

Female choirs, usually consisting of soprano and alto voices, two parts in each, often abbreviated as SSAA, or as soprano I, soprano II, and alto, abbreviated SSA.

Men's choirs, or Male Chorale, usually consisting of two tenors, baritone, and bass, often abbreviated as TTBB (or ATBB if the upper part sings falsetto in alto range). ATBB may be seen in some barbershop quartet music.

Children's choirs, often two-part SA or three-part SSA, sometimes more voices. This includes boy choirs.Boy choirs typically sing SSA or SSAA, sometimes including a tenor part for boys whose voices are changing.

Indian music choral group, takes the elements of western music in Indian music. Madras Youth choir is a pioneer in this.

Choirs are also categorized by the institutions in which they operate:

There are various schools of thought regarding how the various sections should be arranged on stage.

In symphonic choirs it is common (though by no means universal) to order the choir behind the orchestra from highest to lowest voices from left to right, corresponding to the typical string layout.

In a cappella or piano-accompanied situations it is not unusual for the men to be in the back and the women in front; some conductors prefer to place the basses behind the sopranos, arguing that the outer voices need to tune to each other.

More experienced choirs may sing with the voices all mixed. Sometimes singers of the same voice are grouped in pairs or threes. Proponents of this method argue that it makes it easier for each individual singer to hear and tune to the other parts, but it requires more independence from each singer. Opponents argue that this method loses the spatial separation of individual voice lines, an otherwise valuable feature for the audience, and that it eliminates sectional resonance, which lessens the effective volume of the chorus.

For music with double (or multiple) choirs, usually the members of each choir are together, sometimes significantly separated, especially in performances of 16th-century music. Some composers actually specify that choirs should be separated, such as in Benjamin Britten's War Requiem.

Consideration is also given to the spacing of the singers. Studies have found that not only the actual formation, but the amount of space (both laterally and circumambiently) affects the perception of sound by choristers and auditors.[2]

The origins of choral music are found in traditional music, as singing in big groups is extremely widely spread in traditional cultures (both singing in one part, or in unison, like in Ancient Greece, as well as singing in parts, or in harmony, like in contemporary European choral music).[3]

The earliest notated music of western Europe is Gregorian chant, along with a few other types of chant which were later subsumed (or sometimes suppressed) by the Catholic Church. This tradition of unison choir singing lasted from sometime between the times of St. Ambrose (4th century) and Gregory the Great (6th century) up to the present. During the later Middle Ages, a new type of singing involving multiple melodic parts, called organum, became predominant for certain functions, but initially this polyphony was only sung by soloists. Further developments of this technique included clausulae, conductus and the motet (most notably the isorhythmic motet), which, unlike the Renaissance motet, describes a composition with different texts sung simultaneously in different voices. The first evidence of polyphony with more than one singer per part comes in the Old Hall Manuscript (1420, though containing music from the late 14th century), in which there are apparent divisi, one part dividing into two simultaneously sounding notes.

During the Renaissance, sacred choral music was the principal type of formally notated music in Western Europe. Throughout the era, hundreds of masses and motets (as well as various other forms) were composed for a cappella choir, though there is some dispute over the role of instruments during certain periods and in certain areas. Some of the better-known composers of this time include Guillaume Dufay, Josquin des Prez, Giovanni Pierluigi da Palestrina, and William Byrd; the glories of Renaissance polyphony were choral, sung by choirs of great skill and distinction all over Europe. Choral music from this period continues to be popular with many choirs throughout the world today.

The madrigal, a partsong conceived for amateurs to sing in a chamber setting, originated at this period. Although madrigals were initially dramatic settings of unrequited-love poetry or mythological stories in Italy, they were imported into England and merged with the more dancelike balletto, celebrating carefree songs of the seasons, or eating and drinking. To most English speakers, the word madrigal now refers to the latter, rather than to madrigals proper, which refers to a poetic form of lines consisting of seven and eleven syllables each.

The Baroque period in music is associated with the development around 1600 of the figured bass, with dramatic implications in the realm of solo vocal music such as the monodies of the Florentine Camerata and opera. This innovation was in fact an extension of established practice of accompanying choral music at the organ, either from a skeletal reduced score (from which otherwise lost pieces can sometimes be reconstructed) or from a basso seguente, a part on a single staff containing the lowest sounding part.

A new genre was the vocal concertato, combining voices and instruments; its origins may be sought in the polychoral music of the Venetian school. Claudio Monteverdi (1567–1643) brought it to perfection with his Vespers and his Eighth Book of Madrigals,[5] which call for great virtuosity on the part of singers and instruments alike. His pupil Heinrich Schütz (1585–1672) (who had earlier studied with Giovanni Gabrieli) introduced the new style to Germany. Alongside the new music of the seconda pratica, contrapuntal motets in the stile antico or old style continued to be written well into the 19th century.

It should be remembered that choirs at this time were usually quite small and that singers could be classified as suited to church or to chamber singing. Monteverdi, himself a singer, is documented as taking part in performances of his Magnificat with one voice per part.[6]

Independent instrumental accompaniment opened up new possibilities for choral music. Verse anthems alternated accompanied solos with choral sections; the best-known composers of this genre were Orlando Gibbons and Henry Purcell. Grands motets (such as those of Lully and Delalande) separated these sections into separate movements. Oratorio, pioneered by Giacomo Carissimi, extended this concept into concert-length works, usually loosely based on Biblical stories.

The pinnacle of the oratorio is found in George Frideric Handel's works, notably Messiah and Israel in Egypt. While the modern chorus of hundreds had to await the growth of Choral Societies and his centennial commemoration concert, we find Handel already using a variety of performing forces, from the soloists of the Chandos Anthems to larger groups (whose proportions are still quite different from modern orchestra choruses):

Lutheran composers wrote instrumentally accompanied cantatas, often based on choraletunes. While Dieterich Buxtehude was a significant composer of such works, it was largely up to the next generation to undertake cantata cycles on texts for the entire church year. Georg Philipp Telemann wrote choral cantatas for Frankfurt (later published in solo versions as the Harmonische Gottesdienst) and Graupner cycles for Darmstadt, but Johann Sebastian Bach (1685–1750) made a truly monumental contribution: his obituary mentions five complete cycles of his cantatas, of which three, comprising some 200 works, are known today, in addition to motets. Bach himself rarely used the term cantata. Motet refers to his church music without orchestra accompaniment, but instruments playing colla parte with the voices. His works with accompaniment consists of his Passions, Masses, the Magnificat and the cantatas.

Baroque cantata with one voice per part

A point of hot controversy today is the so-called "Rifkin hypothesis," which re-examines the famous "Entwurff" Bach's 1730 memo to the Leipzig City Council (A Short but Most Necessary Draft for a Well Appointed Church Music) calling for at least 12 singers. In light of Bach's responsibility to provide music to four churches and be able to perform double choir compositions with a substitute for each voice, Joshua Rifkin concludes that Bach's music was normally written with one voice per part in mind. A few sets of original performing parts include ripieni who reinforce rather than slavishly double the vocal quartet.

Composers of the late 18th century became fascinated with the new possibilities of the symphony and other instrumental music, and generally neglected choral music. Mozart's choral works, though not as numerous as his works for other media, stand out as some of his greatest (such as the "Great" Mass in C minor and Requiem in D minor, the latter of which is often considered the greatest Requiem Mass of all time). Haydn became more interested in choral music near the end of his life following his visits to England in the 1790s, when he heard various Handel oratorios performed by large forces; he wrote a series of masses beginning in 1797 and his two great oratorios The Creation and The Seasons. Beethoven wrote only two masses, both intended for liturgical use, although his Missa solemnis is suitable only for the grandest ceremonies. He also pioneered the use of chorus as part of symphonic texture with his Ninth Symphony and Choral Fantasia.

A few composers developed a cappella music, especially Bruckner, whose masses and motets startlingly juxtapose Renaissance counterpoint with chromatic harmony. Mendelssohn and Brahms also wrote significant a cappella motets.

The amateur chorus (beginning chiefly as a social outlet) began to receive serious consideration as a compositional venue for the part-songs of Schubert, Schumann, Mendelssohn, Brahms, and others. These 'singing clubs' were often for women or men separately, and the music was typically in four-part (hence the name "part-song") and either a cappella or with simple instrumentation. At the same time, the Cecilian movement attempted a restoration of the pure Renaissance style in Catholic churches.

As in other genres of music, choral music underwent a period of experimentation and development during the 20th century. While few well-known composers focused primarily on choral music, most significant composers of the early century produced some fine examples that have entered the repertoire.

The advent of atonality and other non-traditional harmonic systems and techniques in the 20th century also affected choral music. Serial music is represented by choral works by Arnold Schoenberg, including the anthem "Dreimal Tausend Jahre," while the composer's signature use of sprechstimme is evident in his psalm "De Profundis." Paul Hindemith's distinctive modal language is represented by both his a cappella Mass and his Six Chansons on texts by Rilke, while a more contrapuntally dissonant style comes through in his secular requiem, When Lilacs Last in the Dooryard Bloom'd. Olivier Messiaen also demonstrates dissonant counterpoint in his Cinq Rechants, which tell the Tristan and Isolde story. Charles Ives' psalm settings exemplify the composer's incomparably radical harmonic language. Tone clusters and aleatory elements play a prominent role in the choral music of Krzysztof Penderecki, who wrote the St. Luke Passio, and György Ligeti, who wrote both a Requiem and a separate Lux Aeterna. Milton Babbitt incorporated integral serialism into works for children's chorus, while Daniel Pinkham wrote for choir and electronic tape. Meredith Monk's Panda Chant and Astronaut Anthem explore overtones in an unconventional text setting. Though difficult and rarely performed by amateurs, pieces that demonstrate such unfamiliar idioms have found their way into the repertories of the finest semi-professional and professional choirs around the world.

A choir of more than 30,000 participants performing to an audience of 80,000 on the 25th Estonian Song Festival

At the turn of the 21st century, choral music has received a resurgence of interest partly due to a renewed interest in accessible choral idioms.[citation needed] Multi-cultural influences are found in Osvaldo Golijov's St. Mark Passion, which melds the Bach-style passion form with Latin American street music, and Chen Yi's Chinese Myths Cantata melds atonal idioms with traditional Chinese melodies played on traditional Chinese instruments. Some composers began to earn their reputation based foremost on their choral output, including the highly popular John Rutter and Eric Whitacre. The large scale dramatic works of Karl Jenkins seem to hearken back to the theatricality of Orff, and the music of James MacMillan continues the tradition of boundary-pushing choral works from the United Kingdom begun by Britten, Walton, and Leighton. Meanwhile, composers such as John Williams, known primarily for film scores, and prominent concert orchestral composers such as Augusta Read Thomas, Sofia Gubaidulina, Aaron Jay Kernis, and Thomas Adès also contribute vital additions to the choral repertoire.

A number of traditions originating outside of classical concert music have enriched the choral repertoire as well as provided new outlets to composers:

During the mid 20th century, barbershop quartets began experimenting with combining larger ensembles together into choruses which sing barbershop music in 4 parts, often with staging, choreography and costumes. The first international barbershop chorus contest was held in 1953 and continues to this day.

African and African American choirs have a distinct and passionate sound. They incorporate their culture into the music; have a more upbeat tempo and use traditional instruments. They are also very good at singing slow and soulful renditions.

MB Srinivasan a pioneer in Indian choral music fused the elements of western music in Indian music. The Madras Youth Choir, is the oldest Indian choral music group in India.

Contemporary choirs, such as Rock Choir and London Contemporary Voices in the United Kingdom, and Gotham Rock Choir in America, have become popular since the beginning of the 21st century. They usually perform rock, pop, soul and Motown songs in close-part vocal harmony, often incorporating dance moves.